Fluid jets, such as water jets, generated at relatively high static pressures with a suitable pump and nozzle travel in or through air at a relatively high speed. Such high-speed water-jets, often greater than sonic velocity, are conventionally used in many industrial and commercial processes, such as surface cleaning and preparation, coating removal, ship-hull barnacle removal, and concrete scarification and demolition. In such applications, the productivity of the process is measured by how well and how fast the water-jets are applied to the surface. To maximize the surface coverage of the water-jets, the water-jet nozzle is moved over the surface by hand with a hand tool or by an automated or manual mechanical system to provide the desired nozzle movement. The water jet nozzle or nozzles are often rotated and then moved linearly on the surface. To provide the rotation, the nozzles are attached to a suitable swivel or rotary joint that allows pressurized fluid to be transported from a stationary conduit to a rotating conduit, and the rotation is powered with a suitable motor. The entire system is then linearly moved with a traversing system, such as a vehicle. This process is carried out today in airport runway cleaning in which a large amount of water is consumed and the speed of the process is important. A similar process is applied today in removing marine growth from a ship hull. In both applications, the speed of operation is critical and the productivity is related to or a function of the pressure and flow rate of the water-jets and the movement of the nozzle systems.
In conventional water-jet processes, the water pressure is commonly in thousands of pound per square inch (psi) in household jet wash apparatuses, and tens of thousands of psi in industrial applications. For example, in cleaning heat exchanger tubes and oil well drilling pipes, the water pressure is typically above 20,000 psi and the nozzle rotating speed can reach 1000 revolutions per minute (rpm). In known shipyard barnacle removing processes, the water pressure can exceed 50,000 psi and the rotation speed above 2000 rpm. In such applications, the pump required to provide the desired pressure is no longer a problem and is widely available today, it is the nozzle motion system that becomes important.
At relatively high fluid pressures and relatively high rotation speed, the rotary joint must provide the desired rotary motion and satisfactory fluid sealing. The reliability of the rotating shaft and its dynamic seals are a common concern. As a result, high-pressure high-speed rotary joints are costly and are high-maintenance components, and are avoided if possible.
U.S. Pat. No. 5,794,854 teaches a method of providing linear and orbital movement to a water jet nozzle at high water pressures without the need for a rotary joint. In this prior art, the tube or hose between its anchor and the nozzle is subjected to a prescribed oscillating motion, linearly or orbitally. Water hose and small tubes are ductile enough to accept the applied movement. Thus, a rotary joint is no longer needed. But a motion-generating apparatus must be added to the nozzle system. As a result, a complete nozzle system of this type is rather bulky and complicated.
Another prior art device available for decades is a simple nozzle that provides orbitally oscillating fluid jets at moderate pressures. These nozzles are known as Idrojet (see FIG. 1), Monro Jet (see FIG. 2), and Salo-Jet nozzle (see FIG. 3). In these known nozzles, a pivotally oscillating rotor shaft sends the pressurized fluid from the nozzle chamber through a nozzle orifice to the outside. The oscillating motion of the rotor assembly is provided by the fluid motion inside the nozzle chamber, thus requiring no external power. These nozzles are common and are widely used in current water jet processes at low and moderate water pressures, commonly referred to as jet washer pressures. However, recent attempts have been made to bring up the pressure capability of these orbital nozzles.
These orbital nozzles share a common design and often appear in the shape of a bulb. In applications, the nozzle often shakes excessively due to the orbital jet motion and attempts have been made to isolate such undesirable nozzle shaking motion. One example is shown in International Patent Application WO91/16989 that teaches springs and an external housing to isolate the nozzle shake. The shaking motion of these nozzles is caused by several factors, including the slow orbital motion of the rotor and the jet. In current water-jetting applications, the speed of the water jet motion is critical to high productivity. The three commercially available orbital nozzles cited here all have these related shortcomings.
The quality of the water-jet is another issue that available orbital nozzles fail to address fully. For high productivity at high pressures, the water-jet must be produced with high precision jewel-quality orifices in order to produce coherent and long-lasting water-jets. The size of the orifices determines the energy delivered to the surface and may have to be changed often in an operation. Thus, the ease of changing the nozzle is also connected to high productivity. The commercially available orbital nozzles all use drilled metal orifices and changing the orifice size requires replacement of the entire rotor assembly, that is both inconvenient and not cost effective.